Synthetic leather

ABSTRACT

The present invention provides a synthetic leather including at least a base material (i), an adhesive layer (ii), and a skin layer (iii), wherein both the adhesive layer (ii) and the skin layer (iii) are formed of a urethane resin composition containing an anionic urethane resin having an anionic group concentration of 0.25 mmol/g or less, water, and an anionic surfactant. Preferably, the anionic surfactant is an alkylsulfosuccinate. The anionic group concentration of the anionic urethane resin is preferably within the range of 0.005 to 0.25 mmol/g and more preferably within the range of 0.01 to 0.2 mmol/g.

TECHNICAL FIELD

The present invention relates to a synthetic leather.

BACKGROUND ART

Polyurethane resins have been widely used for producing synthetic leathers (including artificial leathers) because of the mechanical strength and favorable texture thereof. Regarding this application, solvent-based urethane resins containing N,N-dimethylformamide (DMF) have been the mainstream until now. However, against the background of DMF control in Europe, tightening of VOC emission control in China and Taiwan, DMF control in the major apparel makers, and the like, a departure from DMF is required for the urethane resin used for each layer constituting a synthetic leather.

To address such circumstances, urethane resin compositions in which a urethane resin is, for example, dispersed in water have been widely researched (refer to, for example, PTL 1). Regarding skin layers of synthetic leathers, replacement of a solvent base with a water base, as in the invention described in PTL 1, is gradually increasing in the market. However, regarding a urethane resin for an adhesive layer, the shift to the water base has not yet advanced. In addition, regarding skin layers, there are many problems to be addressed, for example, an odor problem due to a neutralizer, a reduction in bleeding materials, and the like, in accordance with the actual circumstances.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. 2007-119749

SUMMARY OF INVENTION Technical Problem

An issue to be addressed by the present invention is the provision of a synthetic leather having a reduced odor and excellent bleeding resistance.

Solution to Problem

The present invention provides a synthetic leather including at least a base material (i), an adhesive layer (ii), and a skin layer (iii), wherein both the adhesive layer (ii) and the skin layer (iii) are formed of a urethane resin composition containing an anionic urethane resin having an anionic group concentration of 0.25 mmol/g or less, water, and an anionic surfactant.

Advantageous Effects of Invention

A synthetic leather according to the present invention has a reduced odor and excellent bleeding resistance.

Using a specific urethane resin for the adhesive layer (ii) and the skin layer (iii) can provide a synthetic leather further having excellent hydrolysis resistance in addition to the above-described effects.

Therefore, the synthetic leather according to the present invention may be used for various applications and, in particular, may be used for applications, such as car interior materials, furniture, and sports shoes, which require high durability and in which replacement of a solvent base with a water base has been considered to be difficult.

DESCRIPTION OF EMBODIMENTS

A synthetic leather according to the present invention includes at least a base material (i), an adhesive layer (ii), and a skin layer (iii).

Both the adhesive layer (ii) and the skin layer (iii) have to be formed of a urethane resin composition containing an anionic urethane resin having an anionic group concentration of 0.25 mmol/g or less, water, and an anionic surfactant.

Setting the anionic group concentration of the urethane resin used for both the adhesive layer (ii) and the skin layer (iii) to be 0.25 mmol/g or less enables the amount of an amine compound which is widely used as a neutralizer to be reduced and enables an odor problem to be suppressed from occurring. In addition, using the anionic surfactant enables water dispersion stability of the urethane resin to be improved even when anionic groups are reduced, and since the anionic groups readily form hydrogen bonds with anionic groups of the urethane resin, a bleeding material can be reduced in quantity. Meanwhile, using a urethane resin composition having a configuration similar to the adhesive layer (ii) and the skin layer (iii) enables excellent adhesiveness between the adhesive layer (ii) and the skin layer (iii) to be provided.

The anionic group concentration of the anionic urethane resin is preferably 0.005 mmol/g or more and more preferably 0.01 mmol/g or more, preferably 0.25 mmol/g or less and more preferably 0.2 mmol/g or less, and preferably within the range of 0.005 to 0.25 mmol/g and more preferably within the range of 0.01 to 0.2 mmol/g since odor can be still further reduced while the water dispersion stability is maintained. In this regard, the anionic group concentration of the anionic urethane resin is a value obtained by dividing the number of moles of an anionic group derived from a raw material used for producing the urethane resin having an anionic group by the total mass of raw materials for constituting the anionic urethane resin.

Examples of the method for introducing the anionic group into the anionic urethane resin include a method in which at least one compound selected from a group consisting of glycol compounds having a carboxy group and compounds having a sulfonyl group is used as a raw material.

Regarding the glycol compounds having a carboxy group, for example, 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolpropionic acid, and 2,2-valeric acid may be used. These compounds may be used alone, or at least two types may be used in combination.

Regarding the compounds having a sulfonyl group, for example, 3,4-diaminobutanesulfonic acid, 3,6-diamino-2-toluenesulfonic acid, 2,6-diaminobenzenesulfonic acid, and N-(2-aminoethyl)-2-aminoethylsulfonic acid may be used. These compounds may be used alone, or at least two types may be used in combination.

Some or all of the carboxy groups and the sulfonyl groups may be neutralized to basic compounds in an aqueous urethane resin composition. Regarding the basic compounds, for example, organic amines such as ammonia, triethylamine, pyridine, and morpholine; alkanolamines such as monoethanolamine and diethylethanolamine; and metal basic compounds containing sodium, potassium, lithium, or calcium may be used.

Regarding the anionic urethane resin contained in the urethane resin composition for forming the adhesive layer (ii) and the skin layer (iii), specifically, for example, a reaction product of the raw material used for producing the urethane resin having an anionic group, a polyisocyanate, a polyol, and an elongation agent may be used.

The amount of the raw material used for producing the urethane resin having an anionic group is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and further preferably 0.3% by mass or more, preferably 10% by mass or less, more preferably 7% by mass or less, and further preferably 4% by mass or less, and preferably within the range of 0.05% by mass to 10% by mass, more preferably within the range of 0.1% by mass to 7% by mass, and further preferably within the range of 0.3% by mass to 4% by mass in the polyol since even further excellent chemical resistance and hydrolysis resistance are obtained.

Regarding the polyisocyanate, for example, aliphatic or alicyclic polyisocyanates such as hexamethylene diisocyanate, lysine diisocyanate, cyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, dimer acid diisocyanate, and norbornene diisocyanate; and aromatic polyisocyanates such as phenylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, polymethylene polyphenyl polyisocyanate, and carbodiimidized diphenylmethane polyisocyanate may be used. These polyisocyanates may be used alone, or at least two types may be used in combination. Of these, regarding the adhesive layer (ii), it is more preferable that at least one polyisocyanate selected from a group consisting of isophorone diisocyanate, toluene diisocyanate, and hexamethylene diisocyanate be used since even further excellent adhesiveness is obtained. Of these, regarding the skin layer (iii), it is more preferable that at least one polyisocyanate selected from a group consisting of isophorone diisocyanate, dicyclohexylmethane diisocyanate, and hexamethylene diisocyanate be used since even further excellent light resistance is obtained

Regarding the polyol, for example, polyether polyols, polyester polyols, polycarbonate polyols, dimer diols, acrylic polyols, and polybutadiene polyols may be used. These polyols may be used alone, or at least two types may be used in combination. Of these, it is preferable that polycarbonate polyols and/or polyether polyols be used, and polycarbonate polyols and/or polypropylene polyols are more preferable since even further excellent chemical resistance and hydrolysis resistance are obtained.

Regarding the polycarbonate polyols, preferably, hexane diol and/or polycarbonate polyols, for which a raw material is ϵ-caprolactone, is used since even further excellent chemical resistance and hydrolysis resistance are obtained.

The number average molecular weight of the polyol is preferably within the range of 500 to 100,000 and more preferably within the range of 800 to 10,000 since even further excellent chemical resistance and mechanical strength are obtained. In this regard, the number average molecular weight of the polyol is a value measured by using a gel-permeation-column chromatography (GPC) method.

Regarding the elongation agent, for example, chain elongation agents having a hydroxy group and chain elongation agents having an amino group, each having a molecular weight of 50 or more and 500 or less, may be used. These may be used alone, or at least two types may be used in combination.

Regarding the chain elongation agents having a hydroxy group, for example, aliphatic polyol compounds such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, hexamethylene glycol, saccharose, methylene glycol, glycerin, and sorbitol; aromatic polyol compounds such as bisphenol A, 4,4′-dihydroxydiphenyl, 4,4′-dihydroxydiphenyl ether, 4,4′-dihydroxydiphenyl sulfone, hydrogenated bisphenol A, and hydroquinone; and water may be used. These chain elongation agents may be used alone, or at least two types may be used in combination.

Regarding the chain elongation agents having an amino group, for example, ethylenediamine, 1,2-propanediamine, 1,6-hexamethylenediamine, piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, isophoronediamine, 4,4′-dicyclohexylmethanediamine, 3,3′-dimethyl-4,4′-dicyclohexylmethanediamine, 1,2-cyclohexanediamine, 1,4-cyclohexanediamine, aminoethylethanolamine, hydrazine, diethylenetriamine, triethylenetetramine, and adipic acid dihydrazide may be used. These chain elongation agents may be used alone, or at least two types may be used in combination.

Regarding the chain elongation agent, preferably, a chain elongation agent having an amino group is used since even further excellent light resistance is obtained, and it is preferable that at least one chain elongation agent selected from a group consisting of ethylenediamine, isophorone diamine, and hydrazine be used.

The amount of the chain elongation agent used is preferably within the range of 0.01% by mass to 20% by mass and more preferably within the range of 0.05% by mass to 10% by mass in the total mass of the raw materials constituting the urethane resin since the durability, the chemical resistance, the hydrolysis resistance, and the light resistance of a coat can be further improved.

Examples of the method for manufacturing the urethane resin include a method in which a urethane prepolymer having an isocyanate group is obtained by reacting the polyisocyanate, the raw material used for producing the urethane resin having an anionic group, and the polyol, the anionic group is neutralized, water and the chain elongation agent are added, and thereafter a reaction is performed. Preferably, these reactions are performed at a temperature of 50° C. to 100° C. for 3 to 10 hours, for example.

The molar ratio [NCO/OH] of the isocyanate group in the polyisocyanate to the total of the hydroxy group and the amino group in the raw material for producing the urethane resin having a hydrophilic group and the polyol for forming the adhesive layer (ii) is preferably 0.8 or more and more preferably 0.9 or more, preferably 1.5 or less and more preferably 1.3 or less, and preferably within the range of 0.8 to 1.5 and more preferably within the range of 0.9 to 1.3 since even further excellent adhesiveness is obtained. Meanwhile, for forming the skin layer (iii), the molar ratio is preferably more than 1.5 and more preferably 1.7 or more, preferably 3 or less and more preferably 2.5 or less, and preferably more than 1.5 and 3 or less and more preferably within the range of 1.7 to 2.5 since even further excellent chemical resistance and hydrolysis resistance are obtained.

In addition, when the urethane resin is produced, an organic solvent may be used. Regarding the organic solvent, for example, ketone compounds such as acetone and methyl ethyl ketone; ether compounds such as tetrahydrofuran and dioxane; acetic acid ester compounds such as ethyl acetate and butyl acetate; nitrile compounds such as acetonitrile; amide compounds such as dimethylformamide and N-methylpyrrolidone; and film-forming auxiliaries such as dipropylene glycol dimethyl ether, diethyl diglycol, and diethyl adipate may be used. These organic solvents may be used alone, or at least two types may be used in combination. Regarding the organic solvent, preferably, acetone and/or a film-forming auxiliary is used. In this regard, it is preferable that the organic solvent other than the film-forming auxiliary be removed by a distillation method or the like when a urethane resin composition is obtained.

The weight average molecular weight of the anionic urethane resin for forming the adhesive layer (ii) is preferably 10,000 or more and more preferably 30,000 or more, preferably 400,000 or less and more preferably 200,000 or less, and preferably within the range of 10,000 to 400,000 and more preferably within the range of 30,000 to 200,000 since even further excellent adhesiveness is obtained. Meanwhile, for forming the skin layer (iii), the molecular weight is preferably 60,000 or more and more preferably 100,000 or more, preferably 500,000 or less and more preferably 300,000 or less, and preferably within the range of 60,000 to 700,000 and more preferably within the range of 100,000 to 500,000 since even further excellent light resistance is obtained. In this regard, the weight average molecular weight of the anionic urethane resin is a value measured by using a gel-permeation-column chromatography (GPC) method.

Regarding the water, ion-exchanged water, distilled water, and the like may be used. The content of the water is preferably within the range of 30% by mass to 90% by mass and more preferably within the range of 35% by mass to 80% by mass in the urethane resin composition from the viewpoint of operability, coating performance, and storage stability.

Regarding the anionic surfactant, for example, alkylsulfosuccinic acid salts, N-acylamino acid salts, lactic acid fatty acid ester salts, fatty acid salts, succinic acid monoglycerides, diacetyltartaric acid monoglycerides, stearic acid tartaric acid esters, stearic acid citric acid esters, citric acid monoglycerides, lecithin, lysolecithin, alkylsulfuric acid salts, polyoxyethylene alkyl ether sulfuric acid salts, acyl N-methyltaurine salts, sodium stearyl fumarate, monoglyceride phosphoric acid salts, and alkyl ether phosphoric acid ester salts may be used. These anionic surfactants may be used alone, or at least two types may be used in combination. Of these, it is preferable that alkylsulfosuccinic acid salts be used since even further excellent water dispersion stability and bleeding resistance are obtained.

Regarding the alkylsulfosuccinic acid salts, for example, compounds including a straight chain or branched alkyl group having 1 to 16 and preferably 2 to 14 carbon atoms may be used, and the number of alkyl groups is preferably within the range of 1 to 3. Of these, it is preferable that dioctylsulfosuccinic acid salts be used since even further excellent water dispersion stability and bleeding resistance are obtained.

Examples of the salts include sodium salts, potassium salts, lithium salts, calcium salts, and ammonium salts.

The amount of the anionic surfactant used is preferably 0.01 parts by mass or more and more preferably 0.1 parts by mass or more, preferably 10 parts by mass or less and more preferably 3 parts by mass or less, and preferably within the range of 0.01 to 10 parts by mass and more preferably within the range of 0.1 to 3 parts by mass relative to 100 parts by mass of the anionic urethane resin since even further excellent water dispersion stability and bleeding resistance are obtained.

The urethane resin composition may contain other additives, as the situation demands, in addition to the anionic urethane resin, the water, and the anionic surfactant.

Regarding the other additives, for example, emulsifiers, coagulants, urethanization catalysts, silane coupling agents, fillers, thixotropy-imparting agents, tackifiers, waxes, heat stabilizers, light resistance stabilizers, fluorescent brighteners, foaming agents, pigments, dyes, conductivity-imparting agents, antistatic agents, moisture permeability improvers, water-repellent agents, oil-repellent agents, hollow foams, flame retardants, water absorbents, moisture absorbents, deodorants, foam stabilizers, blocking inhibitors, hydrolysis inhibitors, and thickeners may be used. These additives may be used alone, or at least two types may be used in combination.

Next, the synthetic leather according to the present invention will be described.

The synthetic leather according to the present invention contains at least a base material (i), an adhesive layer (ii), and a skin layer (iii), and specific examples include the following configurations.

(1) Base material (i), adhesive layer (ii), and skin layer (iii) (2) Base material (i), adhesive layer (ii), intermediate layer, and skin layer (iii) (3) Base material (i), porous layer, adhesive layer (ii), and skin layer (iii) (4) Base material (i), porous layer, adhesive layer (ii), intermediate layer, and skin layer (iii)

Regarding the base material (i), for example, fiber base materials such as polyester fibers, polyethylene fibers, nylon fibers, acrylic fibers, polyurethane fibers, acetate fibers, rayon fibers, polylactic acid fibers, cotton, hemp, silk, wool, glass fibers, carbon fibers, unwoven fabrics of blended yarn or the like of these, woven fabrics, and knit fabrics; the nonwoven fabrics impregnated with a resin such as an polyurethane resin; the nonwoven fabrics further provided with a porous layer; and resin base materials such as thermoplastic urethane (TPU) may be used.

Regarding the porous layer, for example, porous layers formed of solvent-based urethane resin compositions by using a known wet-film-formation method; and aqueous urethane resin compositions made to be porous by a known method may be used.

Regarding the material for forming the intermediate layer, for example, known aqueous urethane resins, solvent-based urethane resins, solventless urethane resins, aqueous acrylic resins, silicone resins, polypropylene resins, and polyester resins may be used. These resins may be used alone, or at least two types may be used in combination.

A surface-treatment layer may be further disposed on the skin layer (iii) to prevent flawing and the like. Regarding the material for forming the surface-treatment layer, for example, known aqueous urethane resins, solvent-based urethane resins, solventless urethane resins, aqueous acrylic resins, silicone resins, polypropylene resins, and polyester resins may be used. These resins may be used alone, or at least two types may be used in combination.

Next, a method for manufacturing a synthetic leather having the configuration in (1) above will be described.

Examples of the method for manufacturing the synthetic leather include a method in which a base material subjected to mold-release treatment is coated with a urethane resin composition for forming a skin layer, a drying step is performed so as to obtain the skin layer (iii), the resulting skin layer (iii) is coated with a urethane resin composition for forming an adhesive layer, drying is performed so as to form the adhesive layer (ii), and the resulting adhesive layer (ii) is bonded to the base material (i). Alternatively, a method in which the skin layer (iii) is coated with a urethane resin composition for forming an adhesive layer, bonding to the base material (i) is performed, and thereafter drying is performed so as to form the adhesive layer (ii) may be adopted.

Examples of the method for applying the urethane resin composition for forming the skin layer or forming the adhesive layer include a method in which an applicator, a roll coater, a spray coater, a T-die coater, a knife coater, a comma coater, or the like is used.

Examples of the method for drying the urethane resin composition include a method in which drying is performed at 40° C. to 130° C. for 1 to 10 minutes. The thickness of each of the resulting adhesive layer (ii) and skin layer (iii) is appropriately set in accordance with the use of the synthetic leather and is, for example, within the range of 0.5 to 100 μm.

After the synthetic leather is produced, as the situation demands, aging may be performed at 30° C. to 100° C. for 1 to 10 days, for example.

As described above, the synthetic leather according to the present invention has a reduced odor and excellent bleeding resistance. A synthetic leather further having excellent hydrolysis resistance in addition to the above-described effects can be obtained by using a specific urethane resin for each of the adhesive layer (ii) and the skin layer (iii).

Therefore, the synthetic leather according to the present invention can be used for various applications and, in particular, can be used for applications, such as car interior materials, furniture, and sports shoes, which require high durability and in which replacement of a solvent base with a water base has been considered to be difficult.

EXAMPLES

The present invention will be described below in further detail with reference to examples.

[Synthesis Example 1] Preparation of Urethane Resin (S-1) Composition for Forming Adhesive Layer

In a four-neck flask provided with an agitator, a reflux condenser tube, a thermometer, and a nitrogen blowing tube, under a nitrogen stream, 200 parts by mass of polypropylene glycol (number average molecular weight: 3,000), 6.4 parts by mass of 2,2-dimethylolpropionic acid (hereafter abbreviated as “DMPA”), and 12 parts by mass of dipropylene glycol dimethyl ether were homogeneously mixed at 70° C., 28 parts by mass of isophorone diisocyanate (hereafter abbreviated as “IPDI”) was added, and a reaction was performed at 100° C. for 6 hours so as to obtain a urethane prepolymer solution having an isocyanate group (NCO/OH=1.1). Subsequently, 4.3 parts by mass of N,N-dimethylethanolamine was added to the urethane prepolymer solution so as to neutralize carboxy groups of the urethane prepolymer. Thereafter, 2 parts by mass of sodium dioctylsulfosuccinate was added and homogeneously mixed. After 441 parts by mass of ion-exchanged water was added, 0.6 parts by mass of 80%-by-mass hydrazine hydrate was added, and a reaction was performed so as to obtain a urethane resin (S-1) composition (nonvolatile content: 35% by mass; and anionic group concentration: 0.20 mmol/g) for forming an adhesive layer.

[Synthesis Example 2] Preparation of Urethane Resin (S-2) Composition for Forming Adhesive Layer

In a four-neck flask provided with an agitator, a reflux condenser tube, a thermometer, and a nitrogen blowing tube, under a nitrogen stream, 200 parts by mass of polypropylene glycol (number average molecular weight: 2,000), 5.6 parts by mass of DMPA, and 12 parts by mass of dipropylene glycol dimethyl ether were homogeneously mixed at 70° C., 27 parts by mass of toluene diisocyanate (hereafter abbreviated as “TDI”) was added, and a reaction was performed at 100° C. for 6 hours so as to obtain a urethane prepolymer solution having an isocyanate group (NCO/OH=1.1). Subsequently, 3.7 parts by mass of N,N-dimethylethanolamine was added to the urethane prepolymer solution so as to neutralize carboxy groups of the urethane prepolymer. Thereafter, 5 parts by mass of sodium dioctylsulfosuccinate was added and homogeneously mixed. After 442 parts by mass of ion-exchanged water was added, 0.7 parts by mass of 80%-by-mass hydrazine hydrate was added, and a reaction was performed so as to obtain a urethane resin (S-2) composition (nonvolatile content: 35% by mass and anionic group concentration: 0.18 mmol/g) for forming an adhesive layer.

[Synthesis Example 3] Preparation of Urethane Resin (S-3) Composition for Forming Adhesive Layer

In a four-neck flask provided with an agitator, a reflux condenser tube, a thermometer, and a nitrogen blowing tube, under a nitrogen stream, 200 parts by mass of polypropylene glycol (number average molecular weight: 2,000), 4 parts by mass of DMPA, and 12 parts by mass of dipropylene glycol dimethyl ether were homogeneously mixed at 70° C., 23 parts by mass of TDI was added, and a reaction was performed at 100° C. for 6 hours so as to obtain a urethane prepolymer solution having an isocyanate group (NCO/OH=1.0). Subsequently, 3.5 parts by mass of N,N-dimethylethanolamine was added to the urethane prepolymer solution so as to neutralize carboxy groups of the urethane prepolymer. Thereafter, 5 parts by mass of sodium dioctylsulfosuccinate was added and homogeneously mixed. After 429 parts by mass of ion-exchanged water was added, 0.8 parts by mass of 80%-by-mass hydrazine hydrate was added, and a reaction was performed so as to obtain a urethane resin (S-3) composition (nonvolatile content: 35% by mass and anionic group concentration: 0.13 mmol/g) for forming an adhesive layer.

[Synthesis Example 4] Preparation of Urethane Resin (S-4) Composition for Forming Adhesive Layer

In a four-neck flask provided with an agitator, a reflux condenser tube, a thermometer, and a nitrogen blowing tube, under a nitrogen stream, 200 parts by mass of polypropylene glycol (number average molecular weight: 2,000) and 6 parts by mass of DMPA were homogeneously mixed at 70° C., 35 parts by mass of IPDI was added, and a reaction was performed at 100° C. for 6 hours so as to obtain a urethane prepolymer solution having an isocyanate group (NCO/OH=1.1). Subsequently, the resulting urethane prepolymer was cooled to 60° C., and 103 parts by mass of acetone was added and homogeneously dissolved. After 4.5 parts by mass of triethylamine was added to the urethane prepolymer solution so as to neutralize carboxy groups of the urethane prepolymer, 2 parts by mass of sodium dioctylsulfosuccinate was added and homogeneously mixed. Subsequently, 454 parts by mass of ion-exchanged water was added, 0.7 parts by mass of 80%-by-mass hydrazine hydrate was added, and a reaction was performed. After the reaction was completed, acetone was removed by distillation under reduced pressure so as to obtain a urethane resin (S-4) composition (nonvolatile content: 35% by mass and anionic group concentration: 0.19 mmol/g) for forming an adhesive layer.

[Synthesis Example 5] Preparation of Urethane Resin (X-1) Composition for Forming Skin Layer

In a four-neck flask provided with an agitator, a reflux condenser tube, a thermometer, and a nitrogen blowing tube, under a nitrogen stream, 100 parts by mass of polypropylene glycol (number average molecular weight: 2,000), 100 parts by mass of polypropylene glycol (number average molecular weight: 1,000), 7 parts by mass of DMPA, and 16 parts by mass of dipropylene glycol dimethyl ether were placed and homogeneously mixed at 70° C. Thereafter, 90 parts by mass of isophorone diisocyanate was added, and a reaction was performed at 100° C. for about 6 hours so as to obtain a urethane prepolymer solution having an isocyanate group (NCO/OH=2.0). Subsequently, 4.7 parts by mass of N,N-dimethylethanolamine was added to the urethane prepolymer solution so as to neutralize carboxy groups in the urethane prepolymer. Thereafter, 3 parts by mass of sodium dioctylsulfosuccinate was added and homogeneously mixed. After 575 parts by mass of ion-exchanged water was added, 10 parts by mass of ethylenediamine was added, and a reaction was performed so as to obtain a urethane resin (X-1) composition (nonvolatile content: 35% by mass and anionic group concentration: 0.18 mmol/g) for forming a skin layer.

[Synthesis Example 6] Preparation of Urethane Resin (X-2) Composition for Forming Skin Layer

In a four-neck flask provided with an agitator, a reflux condenser tube, a thermometer, and a nitrogen blowing tube, under a nitrogen stream, 100 parts by mass of polypropylene glycol (number average molecular weight: 2,000), 100 parts by mass of polypropylene glycol (number average molecular weight: 1,000), 5.5 parts by mass of DMPA, and 15 parts by mass of dipropylene glycol dimethyl ether were placed and homogeneously mixed at 70° C. Thereafter, 85 parts by mass of isophorone diisocyanate was added, and a reaction was performed at 100° C. for about 6 hours so as to obtain a urethane prepolymer solution having an isocyanate group (NCO/OH 32 2.0). Subsequently, 4.2 parts by mass of triethylamine was added to the urethane prepolymer solution so as to neutralize carboxy groups in the urethane prepolymer. Thereafter, 6 parts by mass of sodium dioctylsulfosuccinate was added and homogeneously mixed. After 598 parts by mass of ion-exchanged water was added, 26 parts by mass of isophoronediamine was added, and a reaction was performed so as to obtain a urethane resin (X-2) composition (nonvolatile content: 35% by mass and anionic group concentration: 0.14 mmol/g) for forming a skin layer.

[Synthesis Example 7] Preparation of Urethane Resin (X-3) Composition for Forming Skin Layer

In a four-neck flask provided with an agitator, a reflux condenser tube, a thermometer, and a nitrogen blowing tube, under a nitrogen stream, 200 parts by mass of polycarbonate polyol (number average molecular weight: 2,000), for which the raw material was 1,6-hexanediol, 6.3 parts by mass of DMPA, and 14 parts by mass of dipropylene glycol dimethyl ether were placed and homogeneously mixed at 70° C. Thereafter, 65 parts by mass of isophorone diisocyanate was added, and a reaction was performed at 100° C. for about 6 hours so as to obtain a urethane prepolymer solution having an isocyanate group (NCO/OH=2.0). Subsequently, 5.5 parts by mass of N,N-dimethylethanolamine was added to the urethane prepolymer solution so as to neutralize carboxy groups in the urethane prepolymer. Thereafter, 3 parts by mass of sodium dioctylsulfosuccinate was added and homogeneously mixed. After 523 parts by mass of ion-exchanged water was added, 7 parts by mass of 80%-by-mass hydrazine hydrate was added, and a reaction was performed so as to obtain a urethane resin (X-3) composition (nonvolatile content: 35% by mass and anionic group concentration: 0.17 mmol/g) for forming a skin layer.

[Synthesis Example 8] Preparation of Urethane Resin (X-4) Composition for Forming Skin Layer

In a four-neck flask provided with an agitator, a reflux condenser tube, a thermometer, and a nitrogen blowing tube, under a nitrogen stream, 100 parts by mass of polypropylene glycol (number average molecular weight: 2,000), 100 parts by mass of polypropylene glycol (number average molecular weight: 1,000), and 8 parts by mass of DMPA were placed and homogeneously mixed at 70° C. Thereafter, 93 parts by mass of isophorone diisocyanate was added, and a reaction was performed at 100° C. for about 6 hours so as to obtain a urethane prepolymer solution having an isocyanate group (NCO/OH=2.0). Subsequently, the resulting urethane prepolymer was cooled to 60° C., and 129 parts by mass of acetone was added and homogeneously dissolved. After 6 parts by mass of triethylamine was added to the urethane prepolymer solution so as to neutralize carboxy groups in the urethane prepolymer, 2 parts by mass of sodium dioctylsulfosuccinate was added and homogeneously mixed. Subsequently, 581 parts by mass of ion-exchanged water was added, 10 parts by mass of 80%-by-mass hydrazine hydrate was added, and a reaction was performed. After the reaction was completed, acetone was removed by distillation under reduced pressure so as to obtain a urethane resin (X-4) composition (nonvolatile content: 35% by mass and anionic group concentration: 0.20 mmol/g) for forming a skin layer.

[Comparative Synthesis Example 1] Preparation of Urethane Resin (SR-1) Composition for Forming Adhesive Layer

In a four-neck flask provided with an agitator, a reflux condenser tube, a thermometer, and a nitrogen blowing tube, under a nitrogen stream, 200 parts by mass of polypropylene glycol (number average molecular weight: 2,000) and 15 parts by mass of DMPA were homogeneously mixed at 70° C., 52 parts by mass of IPDI was added, and a reaction was performed at 100° C. for 6 hours so as to obtain a urethane prepolymer solution having an isocyanate group (NCO/OH=1.1). Subsequently, the resulting urethane prepolymer was cooled to 60° C., and 114 parts by mass of acetone was added and homogeneously dissolved. After 11.3 parts by mass of triethylamine was added to the urethane prepolymer solution so as to neutralize carboxy groups in the urethane prepolymer, 2 parts by mass of sodium dioctylsulfosuccinate was added and homogeneously mixed. Subsequently, 501 parts by mass of ion-exchanged water was added, 1.1 parts by mass of 80%-by-mass hydrazine hydrate was added, and a reaction was performed. After the reaction was completed, acetone was removed by distillation under reduced pressure so as to obtain a urethane resin (SR-1) composition (nonvolatile content: 35% by mass and anionic group concentration: 0.42 mmol/g) for forming an adhesive layer.

[Comparative Synthesis Example 2] Preparation of Urethane Resin (SR-2) Composition for Forming Adhesive Layer

In a four-neck flask provided with an agitator, a reflux condenser tube, a thermometer, and a nitrogen blowing tube, under a nitrogen stream, 200 parts by mass of polypropylene glycol (number average molecular weight: 2,000) and 6 parts by mass of DMPA were homogeneously mixed at 70° C., 35 parts by mass of IPDI was added, and a reaction was performed at 100° C. for 6 hours so as to obtain a urethane prepolymer solution having an isocyanate group (NCO/OH=1.1). Subsequently, the resulting urethane prepolymer was cooled to 60° C., and 103 parts by mass of acetone was added and homogeneously dissolved. After 4.5 parts by mass of triethylamine was added to the urethane prepolymer solution so as to neutralize carboxy groups in the urethane prepolymer, 2 parts by mass of nonionic emulsifier (“ADEKA Pluronic F-68” produced by ADEKA Corporation, hereafter abbreviated as “nonionic”) was added and homogeneously mixed. Subsequently, 454 parts by mass of ion-exchanged water was added, 0.7 parts by mass of 80%-by-mass hydrazine hydrate was added, and a reaction was performed. After the reaction was completed, acetone was removed by distillation under reduced pressure so as to obtain a urethane resin (SR-2) composition (nonvolatile content: 35% by mass and anionic group concentration: 0.19 mmol/g) for forming an adhesive layer.

[Comparative Synthesis Example 3] Preparation of Urethane Resin (XR-1) Composition for Forming Skin Layer

In a four-neck flask provided with an agitator, a reflux condenser tube, a thermometer, and a nitrogen blowing tube, under a nitrogen stream, 100 parts by mass of polypropylene glycol (number average molecular weight: 2,000), 100 parts by mass of polypropylene glycol (number average molecular weight: 1,000), and 20 parts by mass of DMPA were placed and homogeneously mixed at 70° C. Thereafter, 133 parts by mass of isophorone diisocyanate was added, and a reaction was performed at 100° C. for about 6 hours so as to obtain a urethane prepolymer solution having an isocyanate group (NCO/OH=2.0). Subsequently, the resulting urethane prepolymer was cooled to 60° C., and 151 parts by mass of acetone was added and homogeneously dissolved. After 15 parts by mass of triethylamine was added to the urethane prepolymer solution so as to neutralize carboxy groups in the urethane prepolymer, 2 parts by mass of sodium dioctylsulfosuccinate was added and homogeneously mixed. Subsequently, 683 parts by mass of ion-exchanged water was added, 15 parts by mass of 80%-by-mass hydrazine hydrate was added, and a reaction was performed. After the reaction was completed, acetone was removed by distillation under reduced pressure so as to obtain a urethane resin (XR-1) composition (nonvolatile content: 35% by mass and anionic group concentration: 0.42 mmol/g) for forming a skin layer.

[Comparative Synthesis Example 4] Preparation of Urethane Resin (XR-2) Composition for Forming Skin Layer

In a four-neck flask provided with an agitator, a reflux condenser tube, a thermometer, and a nitrogen blowing tube, under a nitrogen stream, 100 parts by mass of polypropylene glycol (number average molecular weight: 2,000), 100 parts by mass of polypropylene glycol (number average molecular weight: 1,000), and 8 parts by mass of DMPA were placed and homogeneously mixed at 70° C. Thereafter, 93 parts by mass of isophorone diisocyanate was added, and a reaction was performed at 100° C. for about 6 hours so as to obtain a urethane prepolymer solution having an isocyanate group (NCO/OH=2.0). Subsequently, the resulting urethane prepolymer was cooled to 60° C., and 129 parts by mass of acetone was added and homogeneously dissolved. After 6 parts by mass of triethylamine was added to the urethane prepolymer solution so as to neutralize carboxy groups in the urethane prepolymer, 2 parts by mass of the nonionic was added and homogeneously mixed. Subsequently, 681 parts by mass of ion-exchanged water was added, 10 parts by mass of 80%-by-mass hydrazine hydrate was added, and a reaction was performed. After the reaction was completed, acetone was removed by distillation under reduced pressure so as to obtain a urethane resin (XR-2) composition (nonvolatile content: 35% by mass and anionic group concentration: 0.20 mmol/g) for forming a skin layer.

[Example 1] <Production of Synthetic Leather>

A mixture liquid composed of 100 parts by mass of urethane resin (X-1) composition for forming a skin layer obtained in Synthesis example 4, 10 parts by mass of water-dispersible black pigment (“Dilac HS-9530” produced by DIC Corporation), and 1 part by mass of association-type thickener (“Hydran assister T10” produced by DIC Corporation) was applied to flat release paper (“DN-TP-155T” produced by Ajinomoto Co., Inc.) so that the film thickness after drying became 30 μm, drying was performed at 70° C. for 2 minutes, and drying was further performed at 120° C. for 2 minutes.

Subsequently, a mixture liquid composed of 100 parts by mass of urethane resin (S-1) composition for forming adhesive layer obtained in Synthesis example 1, 1 part by mass of association-type thickener (“Hydran assister T10” produced by DIC Corporation), and 9 parts by mass of polyisocyanate-based cross-linking agent (“Hydran assister C5” produced by DIC Corporation) was applied so that the film thickness after drying became 50 μm, and drying was performed at 70° C. for 3 minutes. Immediately after drying was performed, polyurethane-impregnated nonwoven fabric was bonded, heat treatment was performed at 120° C. for 2 minutes, and aging was performed at 50° C. for 2 days. Subsequently, the release paper was peeled so as to obtain a synthetic leather.

Examples 2 to 9 and Comparative Examples 1 to 6

Synthetic leathers were obtained in the same manner as in Example 1 except that the types of the respective urethane resin compositions for forming a skin layer used and the respective urethane resin compositions for forming an adhesive layer used were changed to those described in Tables 1 to 3.

[Method for Measuring Number Average Molecular Weight and Weight Average Molecular Weight]

Each of the number average molecular weight of the polyol used in the synthesis example and the weight average molecular weight of the urethane resin obtained in the synthesis example was a value obtained by performing measurement under the following conditions by using a gel-permeation-column chromatography (GPC) method.

Measuring Apparatus: High Speed GPC Apparatus (“HLC-8220 GPC” Produced by Tosoh Corporation)

Column: the following columns produced by Tosoh Corporation were used while being connected in series.

-   -   “TSKgel G5000” (7.8 mm I.D.×30 cm)×1 unit     -   “TSKgel G4000” (7.8 mm I.D.×30 cm)×1 unit     -   “TSKgel G3000” (7.8 mm I.D.×30 cm)×1 unit     -   “TSKgel G2000” (7.8 mm I.D.×30 cm)×1 unit         Detector: RI (differential refractometer)         Column temperature: 40° C.         Eluant: tetrahydrofuran (THF)         Flow rate: 1.0 mL/min         Injection rate: 100 μL (tetrahydrofuran solution having a sample         concentration of 0.4% by mass)         Standard sample: the calibration curve was formed by using the         following standard polystyrenes

(Standard Polystyrene)

“TSKgel Standard polystyrene A-500” produced by Tosoh Corporation

“TSKgel Standard polystyrene A-1000” produced by Tosoh Corporation

“TSKgel Standard polystyrene A-2500” produced by Tosoh Corporation

“TSKgel Standard polystyrene A-5000” produced by Tosoh Corporation

“TSKgel Standard polystyrene F-1” produced by Tosoh Corporation

“TSKgel Standard polystyrene F-2” produced by Tosoh Corporation

“TSKgel Standard polystyrene F-4” produced by Tosoh Corporation

“TSKgel Standard polystyrene F-10” produced by Tosoh Corporation

“TSKgel Standard polystyrene F-20” produced by Tosoh Corporation

“TSKgel Standard polystyrene F-40” produced by Tosoh Corporation

“TSKgel Standard polystyrene F-80” produced by Tosoh Corporation

“TSKgel Standard polystyrene F-128” produced by Tosoh Corporation

“TSKgel Standard polystyrene F-288” produced by Tosoh Corporation

“TSKgel Standard polystyrene F-550” produced by Tosoh Corporation

[Method for Evaluating Odor]

The synthetic leather obtained in each of the examples and the comparative examples was placed in a closed container and was left to stand for 24 hours under the condition of a temperature of 80° C. Thereafter, the lid was opened, and an odor was examined and rated as described below.

“B”: there was a slight odor

“C”: there was a strong odor

[Method for Evaluating Bleeding Resistance]

The synthetic leather obtained in each of the examples and the comparative examples was left to stand for five weeks under the conditions of a temperature of 70° C. and a humidity of 95%. Thereafter the appearance was observed and rated as described below.

“A”: there was no irregularity in the appearance

“B”: a small amount of bleeding material was formed on the surface

“C”: a large amount of bleeding material was formed on the surface

[Method for Evaluating Hydrolysis Resistance]

The synthetic leather obtained in each of the examples and the comparative examples was left to stand for five weeks under the conditions of a temperature of 70° C. and a humidity of 95%. Thereafter appearance observation and finger touch were performed and rated as described below.

“A”: there was no irregularity in the appearance and the finger touch

“B”: the appearance was changed in glossiness, but no irregularity was found by finger touch

“C”: the appearance was changed in glossiness, and stickiness was recognized

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Adhesive Type of urethane resin (S-1) (S-2) (S-3) (S-1) (S-2) layer (ii) composition for forming adhesive layer Anionic group 0.2  0.18 0.13 0.2  0.18 concentration of urethane resin (mmol/g) Anionic surfactant SDS SDS SDS SDS SDS Skin Type of urethane resin (X-1) (X-1) (X-1) (X-2) (X-2) layer (iii) composition for forming skin layer Anionic group 0.18 0.18 0.18 0.14 0.14 concentration of urethane resin (mmol/g) Anionic surfactant SDS SDS SDS SDS SDS Evaluation of odor A A A A A Evaluation of bleeding A A A A A resistance Evaluation of hydrolysis A A A A A resistance

TABLE 2 Comparative Example 6 Example 7 Example 8 Example 9 example 1 Adhesive Type of urethane (S-1) (S-3) (S-1) (S-4) (SR-1) layer (ii) resin composition for forming adhesive layer Anionic group 0.2  0.13 0.2 0.19 0.42 concentration of urethane resin (mmol/g) Surfactant SDS SDS SDS SDS SDS Skin Type of urethane (X-3) (X-3) (X-4) (X-4) (XR-1) layer (iii) resin composition for forming skin layer Anionic group 0.17 0.17 0.2 0.2  0.42 concentration of urethane resin (mmol/g) Surfactant SDS SDS SDS SDS SDS Evaluation of odor A A A A C Evaluation of bleeding A A A A A resistance Evaluation of hydrolysis A A A A C resistance

TABLE 3 Comparative Comparative Comparative Comparative Comparative example 2 example 3 example 4 example 5 example 6 Adhesive Type of urethane (SR-2) (S-1) (S-1) (SR-1) (SR-2) layer (ii) resin composition for forming adhesive layer Anionic group 0.19 0.2  0.2 0.42 0.19 concentration of urethane resin (mmol/g) Surfactant nonionic SDS SDS SDS nonionic Skin Type of urethane (XR-2) (XR-1) (XR-2) (X-1) (X-1) layer (iii) resin composition for forming skin layer Anionic group 0.2  0.42 0.2 0.18 0.18 concentration of urethane resin (mmol/g) Surfactant nonionic SDS nonionic SDS SDS Evaluation of odor A C A C A Evaluation of bleeding C A C A C resistance Evaluation of hydrolysis A B A B A resistance

In this regard, “SDS” in Tables 1 to 3 represents sodium dioctylsulfosuccinate.

According to Examples 1 to 9, the synthetic leather according to the present invention had a reduced odor and had excellent abrasion resistance, bleeding resistance, and hydrolysis resistance.

Meanwhile, in the aspect of Comparative example 1 in which the anionic urethane resin having an anionic group concentration beyond the range specified according to the present invention was used for both the adhesive layer (ii) and the skin layer (iii), there was an odor, and the hydrolysis resistance was poor.

In the aspect of Comparative example 2 in which the urethane resin composition containing a nonionic surfactant instead of the anionic surfactant was used for both the adhesive layer (ii) and the skin layer (iii), the bleeding resistance was poor.

In the aspect of Comparative example 3 in which the anionic urethane resin having an anionic group concentration beyond the range specified according to the present invention was used for only the skin layer (ii), there was an odor.

In the aspect of Comparative example 4 in which the nonionic surfactant instead of the anionic surfactant was used for only the skin layer (ii), the bleeding resistance was poor.

In the aspect of Comparative example 5 in which the anionic urethane resin having an anionic group concentration beyond the range specified according to the present invention was used for only the adhesive layer (ii), there was an odor.

In the aspect of Comparative example 6 in which the nonionic surfactant instead of the anionic surfactant was used for only the adhesive layer (ii), the bleeding resistance was poor. 

1. A synthetic leather comprising at least a base material (i), an adhesive layer (ii), and a skin layer (iii), wherein both the adhesive layer (ii) and the skin layer (iii) are formed of a urethane resin composition containing an anionic urethane resin having an anionic group concentration of 0.25 mmol/g or less, water, and an anionic surfactant.
 2. The synthetic leather according to claim 1, wherein the anionic surfactant is an alkylsulfosuccinate. 